JSFiddle - React, Tailwind, and code Playground

HTML

<div id="segment">
  <div id="text1">Hello, <b>how</b> are you?</div>
  <div id="text2"><b>Hello</b>, how are you?</div>
</div>

JavaScript

var text1 = document.querySelector('#text1').innerHTML;
var text2 = document.querySelector('#text2').innerHTML;
document.querySelector('#text1').innerHTML = highlightLetters(text1, 0,5);
document.querySelector('#text2').innerHTML = highlightLetters(text2, 0,5);

function highlightLetters(segmentHTML, startPos, endPos) {

    return "<span style='background-color:pink;'>" + segmentHTML.slice(startPos, endPos) + "</span>" + segmentHTML.slice(endPos);
  }